A device for determining maximum permeability direction and magnitude of permeability of an earth formation, comprising a housing having a planar surface, a fluid-injecting passageway in said housing in open registry with said surface, a plurality of fluid-monitoring ports in said housing in open registry with said surface, with said fluid-monitoring ports being spaced apart from one another and said fluid-injecting passageway in a predetermined array, seal means carried by said housing in an abutting relationship with said surface for providing a substantially fluid-tight seal with said earth formation when said housing is positioned in a contiguous relationship with a surface of said earth formation, said seal means having a plurality of apertures therethrough in respective registry with said fluid-injecting passageway and each of said plurality of fluid-monitoring ports, a fluid reservoir means coupled to said fluid-injecting passageway for injecting a fluid into said earth formation, at least one of a fluid flow measuring means and a fluid pressure measuring means, and means selectively coupling said at least one of said measuring means to each of the fluid-monitoring ports for selectively measuring said at least one of pressure and flow characteristics in a selected manner of the injected fluid emanating from said earth formations into said fluid-monitoring ports.